The invention relates to a safety helmet comprising:                an outer shell in the form of a crown made from shock-resistant plastic material,        a headband arranged inside the crown and composed of a neckband at the rear and a securing strap at the front,        an adjustment mechanism provided with at least one rotary adjustment knob to adjust the headband to the size of the user's head,        and a latch designed to occupy a latched position or an unlatched position to respectively prevent and allow driving of the knob in rotation.        